Switch no longer charging or booting

Yesterday, connected the switch to a charger after playing a game for a while, and it would not charge (attempted at 15%). It did not start charging, but kept operating and drained until it died. The port it was connected to on the charger no longer works, and the switch is not booting anymore. On battery and charger, no signs of life at all despite a constant 8W draw at 15V.

I’ve removed the motherboard, and have been trying to debug the fault. To start, with just the battery connected, VSYS is at ~2.9V (same as the battery). Connecting a 5V supply, VBUS is not passed through the fets to the BQ24193, and VSYS remains the same. Connecting a 15V capable supply, it requests 15V successfully and passes VBUS to the BQ24193. If the battery is disconnected, VSYS then comes up to 4.2V, but the BQ24193 and MAX77620 start heating up, with the MAX77620 getting to nearly 80C° pretty quickly. If the battery is connected, the battery voltage jumps up by about 100mV, which seems to indicate to me that charging is actually functioning as normal. However with the battery connected, VSYS only comes up to 3.5V instead of 4.2V. It does not show any signs of life in either of these cases.

In terms of shorts, nothing at the BQ24193 appears to have any, however the 3.3V and 1.8V rails at the M92T36 appear shorted, and show up at 20mV and 430mV respectively (when using 15V supply).
The caps by the 3.3V regulator next to the audio chip are shorted on the pair, but the third that’s rotated 90° is not shorted.
By the P13USB, the large capacitor is also showing up as shorted.
It seems pretty clear that the 3.3V rail is shorted somehow.

At the MAX77620, the 1.8V, 1.0V (VDD_CPU_1V0), 3.3V, and 1.0V (VDD_1V0) rails all have shorts, and don’t come up normally. Some of them have decent voltages, while others don’t. The corner of the chip closest to the 3.3V cap is the hottest, which makes me think that the overall fault is something in the 3.3V rail that’s messing up the rest of them

Worth noting, this behavior is all occurring immediately as power is applied. I am not pressing any buttons or shorting pins to attempt boot, it just starts drawing this much power the moment it’s plugged in even without a battery connected. With no battery, the draw is about 5-6W, compared to the 7-8W seen with the battery connected.

I’m going to try injecting VSYS directly to see what happens, but I feel like the 3.3V rail is where I need to start. I think that either the MAX77620 might have a short at one of the rails generated using 3.3V, or the CPU itself might. I think removing the MAX77620 will give a better idea of what’s happening.

what are the resistance to ground from 3.3v and 1.8v when nothing connect ?

About 0.2Ω. I’ve since done my testing, and removing the MAX77620, M92T36, and P13 ICs (plus the 3.3v regulator) none of these have impacted the 3.3V short to ground.

Worth noting is the fact that the CPU was also experiencing heating.

By removing the 3.3V regulator and MAX77620, I was able to get the board into a state which confirmed functional battery charging, although it was stuck at 15V and wouldn’t drop any lower.

All things considered, since all of the alternative possible offenders have been removed, I see no other possibility other than the CPU itself for the shorts.

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